This invention relates to a method for measuring the protein content in grain and, more particularly, to a method of measuring the protein content of whole grain kernels.
The protein content of grain samples as well as the oil and water content of the samples has been measured by systems in the prior art by grinding a sample of the grain to particulate form, irradiating the grain sample with near infrared light, detecting the reflectivity of the sample at narrow band wavelengths in the near infrared spectrum to obtain raw reflectance data. The reflectance data is converted to data representing log 1/R, in which R is the reflectivity. From the log 1/R data, the first or second derivative is determined. The first or second derivative values are inserted into equations in which the coefficients are determined by linear regression on known samples. The resulting values give accurate measurements of the oil, protein and water content of the grain samples, provided the particle size of the particles in the sample are uniform and are sufficiently small.
Prior to the present invention, it has been difficult to obtain accurate measurements of the grain constituents without first grinding the grain.
In prior art methods of measuring grain samples, the reflectance or transmittance of the sample was measured at wavelengths at which relatively strong absorbance by the constituents of the grain sample occurred. The wavelengths selected for measurement were restricted to relatively long near infrared wavelengths in the range of 1600 nanometers to 2500 nanometers. While the grain constituents were known to absorb at shorter near infrared wavelengths, the shorter wavelengths were not used because they yielded results which were less accurate than the measurements at the longer wavelengths. The measurements at the longer wavelengths were quite accurate for ground grain samples.